1. Field of the Invention
The present invention relates to a waiting circuit for a portable terminal of a mobile and personal cellular system such as personal handy-phone system (PHS).
2. Background of the Invention
Recently, the use of a personal handy-phone system (PHS), the personal digital cellular (PDC) and other personal mobile and cellular systems have greatly expanded. A waiting reception mode is usually employed in order to decrease the electrical power consumption, because power consumption is one of the most important factors to consumers other than size and the light weight.
The PHS system, uses a multi-carrier 4-time-slots-division-multiple-access (4-TDMA), a transfer manner of time-division-duplex (TDD) and a modulation manner of .pi./4 shift quadrature-phase-shift-keying (QPSK), so each of the users communicates through a time slot different from the other users' time-slots. When not in the communication mode, the portable terminal is set in a sleep-mode in which electrical power is intermittently supplied, for example every 1.2 seconds only to a waiting circuit which detects whether there is a message for the terminal. Other circuits are sleeping or are stopped by stopping the power supply to the circuits. The waiting circuit generates start signal when a message is found so that the electrical power is supplied to other circuits for receiving the message. When no message is detected, the sleep-mode is continued.
FIG. 12 shows a conventional portable terminal, in which there is a waiting circuit 100, a receiver 110 for converting a signal received by an antenna into a intermediate frequency signal, a demodulator 120 for demodulating an output from the receiver 110, a TDMA controller 130 for receiving an output from the demodulator 120, a CPU 140 for controlling the total circuits including the above TDMA controller 130, a detector 101 for detecting a message to the terminal from the intermediate frequency signal and a waiting control circuit 102 for generating the start signal to the TDMA controller 130 and the CPU 140 in response to an output from the detector 101.
When in a sleep-mode, the electrical power is supplied in predetermined time intervals to the receiver 110 and the waiting circuit 100 for detecting a message to the terminal by detector 101. When no message is detected, the circuits 100 and 110 are cut off from the power supply and place in the sleep mode again. When a message is detected, the circuit 102 generates a start signal for supplying the electrical power to the circuits 120, 130 and 140 so that the message can be received. However, the waiting circuit 100 continues in the sleep-mode when the message is not received.
FIG. 13 shows a conventional waiting circuit 100 using a matched filter 104. The matched filter 104 calculates a correlation between the demodulated signal and a coefficient identical to the terminal. The waiting circuit 100 includes a demodulator 103 for demodulating the intermediate frequency signal from the receiver 110 into a baseband signal and for outputting the demodulated signal to the matched filter 104. The matched filter 104 outputs the correlation results to a judgment portion 105 which judges whether the correlation result is higher than a threshold or not and outputs an output when higher. The waiting control circuit 102 outputs the start signal when the correlation is higher. The message can be quickly detected because of the matched filter 104. However, a demodulator is necessary. A demodulator is large in size and consumes a lot of electric power. If the demodulator were omitted by directly inputting the output from the demodulator 120 to the matched filter 104, the demodulator 120 must always be supplied with power. This would cause a substantial amount of power to be consumed.